Cooling arrangement for oil-filled electric transformers or reactors



March 12, 1968 w. JAN ETAL 3,372,733

COOLING ARRANGEMENT FOR OILFILLED ELECTRIC TRANSFORMERS OR REAC'I'ORSFlled May 17, 1965 5 Sheets-Sheet 1 WILHELM JAN JOHANNES REITBAUER.IIIIIIIZ .l KNVENTORS FIG. I.

JIIIIZIZIII.

FIG. 3.

March 12, 1968 w. JAN ETAL COOLING ARRANGEMENT FOR OIL-FILLED ELECTRICTRANSFORMERS OR REACTORS Filed May 17, 1965 5 Sheets-Sheet 5 FIG. 7.

INVENTORS WILHELM JAN JOHANNES REITBAUER United States Patent COOLINGARRANGEMENT FOR OIL-FILLED ELECTRIC TRANSFORMERS OR REACTORS WilhelmJan, Graz, Styria, and Johannes Reitbauer, Weiz,

Styria, Austria, assignors to Elin-Union Aktiengesellschaft furElektrische Industrie, Vienna, Austria Filed May 17, 1965, Ser. No.456,196

Claims priority, application Austria, May 20, 1964,

7 Claims. (Cl. 165-47) The present invention relates to a coolingarrangement for oil-filled electric transformers or reactors, and moreparticularly to such an arrangement wherein vertical sections of thecooling risers are arranged between the legs of horizontal, U-shapeddistributing and collecting header members.

In designing oil-cooled transformers or reactors it is a known measureto remove or dissipate the heat resulting from power losses, by means ofself-cooling radiators (having natural air circulation) or radiatorscooled by ventilators (with forced air circulation). Since, however, thecapacities installed in transformer units increase continually, itbecomes increasingly difiicult to dissipate the heat by the usualradiator cooling. In many cases a change has been made to cooling withoil-water coolers.

Forced circulation of the transformer oil through a water coolernecessitates, however, a considerable expenditure of pumpinginstallations and has, moreover, the great disadvantage that it isnecessary to put the transformer out of service if troubles occur in thepumping installation, as the attained self-cooling is not sufficient todissipate the heat produced by transformer losses.

The same applies to forced cooling by means of fans, even if theradiators are designed in such cases so that it is at least possible tooperate the transformer with a partial load, should the transformer fansfail. The trend is, therefore, to dissipate the heat resulting fromtransformer losses, as far as possible, exclusively by natural aircirculation along the cooling surfaces of the radiators, and to providefans only for producing an additional air circulation during peak loads.

It is the object of this invention to provide a radiator constructionand a cooling arrangement which makes it possible to dissipate thetransformer-loss heat by natural cooling alone, even when using largetransformer units.

The present invention relates to a cooling arrangement for dissipatingthe heat produced by losses in oil-filled electric transformers orreactors, having a plurality of vertical riser groups or sections(cooling pipes) which are fed with the tank oil to be cooled by way ofhorizontal U-shaped distributing and collecting header members,connected to the transformer tank at the middle of the base line of theU, directly or by the intermediary of a further main distributing andcollecting header pipe, wherein one of the main features resides in thatthe U- shaped distributing and collecting header members for theindividual vertical riser groups or sections are horizontally situated,and that these riser sections are arranged between the two legs of theU-shaped header members.

The various objects, features and attendant advantages of the presentinvention will become more apparent from the following description of apreferred embodiment of the transformer cooling arrangement according tothis invention, when considered in conjunction with the accompanyingdrawings, wherein FIG. 1 is a side elevational view of a transformerradiator element incorporating the cooling arrangement of this invention(the transformer tank being omitted);

FIG. 2 is a top elevational view of the radiator element according toFIG. 1;

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FIG. 3 is an enlarged partial view of a constructional detail, showingthe connection between a U-shaped header and one of the riser sections;

FIG. 4 is a side elevational view of an arrangement for supplying withoil a plurality of radiator elements;

FIG. 5 is a top elevational view of the set-up according to FIG. 4;

FIG. 6 is a sectional, partial view of a structural detail, taken alongline 6-6 of FIG. 4; and

FIG. 7 is a side view of the cooling arrangement of FIGS. 4 to 6, viewedin the axial direction of the main distributing and collecting headers,toward the first group of radiator elements.

In the FIGS. 1 and 2, illustrating a first preferred embodiment, numeral1 identifies a top (distributing) header pipe or member and 5 a bottom(collecting) header pipe of a radiator element comprising vertical risersections (cooling pipes) 2, 3 and 4. In accordance with the invention,the header members 1 and 5 are horizontal U-shaped bent pipes (see FIG.2) which, on the base line of the U, are connected by means of flanges 6and shut-off devices 7 to a transformer tank wall 8 (the rest of thetank has been omitted for the sake of clarity), and include between thelegs of the U the vertically disposed inner risers 2, intermediaterisers 3 and outer risers 4. The outermost riser section 4 receives oilfrom and de livers oil to the header members 1, 5 through pipe elbows 9attached to respective limbs of the U-shaped header members 1 and 5, atthe top and the bottom, respectively.

As indicated in FIG. 3, an.innermost riser section 10 may be connectedto the header members 1, 5 by vertical short pieces of pipe 11 welded tothe basis of the U- shaped header members.

A radiator block built up in such a manner, as shown in FIGS. 1 and 2,is supported by C-shaped cantilever beams 12 having flanges 13, 14 whichare directed toward the radiator block. The vertical load resulting atthe bottom connecting point from the above-mentioned attachment of theradiator block is taken up by structural steel plates 15 welded to thetank wall 8, or to stiffening ribs of the transformer tank.

For forced cooling, fans 17 (see FIG. 1) having suitable mountingflanges 16 are provided which, in the illustrated, preferred andexemplary embodiment, blow cooling air in vertical direction. In FIG. 2,numerals 18, 19 identify on the header 5 a terminal box, and itsattachment to the structure, for the fan motors.

The U-shaped header members 1, 5 have a cross-section tapering off fromthe feeding point 6 for the innermost riser section 10, or the innersection 2, towards the outermost riser, e.g. 4 (declining top edge ofheader pipe 1 and declining bottom edge of header pipe 5, respectively)in order to keep constant as far as possible the oil-flow velocity inthese pipes. 1

It should be mentioned that oil flow or circulation in each radiatorelement or block is the result of the wellknown, so-called thermosiphoneffect, that is, natural circulation owing to the weight differencebetween the heated-up and the cooled-down transformer oil. The hot oilrises in the transformer owing to the said effect, is then led to theindividual cooling elements or riser sections by way of the distributingheader pipe, whereupon it is cooled down in the riser sections. The oildescends by its increased weight and is then allowed to return to thebottom of the transformer tank by way of the collecting header pipe.

This is a natural, automatic circulation, as against the forcedcirculation mentioned in the introduction, making use of pumping meansand separate water coolers. The latter are dispensed with in thenatural-circulation system provided in the inventive arrangement. Therate and efficiency of the inventive oil circulation may be increased(if necessary at all) by blowing air onto the radiator elements with theaid of the forced-cooling fans. This may be required in the case of fullload, or for shortperiod overloads of the transformer.

Whenthe fans are energized, the air flow along the individual coolingelements or riser sections is accelerated so that heat dissipation isincreased within the sections. This expedient is also used inconventional radiators having so-called forced air cooling.

The FIGS. 4 and show a second preferred embodiment, with the supply of aplurality of radiator blocks as illustrated in FIGS. 1 and 2 taken froma common main header. Such an arrangement will be found appropriate ifthe radiators are supported by separate fundaments or bases (separatelyinstalled cooler units), making it possible to series-connect severalradiator blocks with respect to the oil flow from and back to thetransformer tank.

It will be noted that FIGS. 4 and 5 are reversed as to the left andright-hand sides of the illustration, as compared to FIGS. 1 and 2 (oilconnections from the right and the left, respectively, in theaforementioned views).

In this embodiment the hot oil is supplied to the various radiatorblocks through a main distributing header 21 and the cooled oil isreturned to the transformer tank through a main collecting header 22. Inorder to keep constant the velocity of the oil stream, the maindistributing header 21 tapers off outwards, as shown. Likewise, the maincollecting header 22 has a narrowing crosssection; moreover, it has aslight slope towards the transformer tank, that is, the right-hand sideof FIGS. 4 and 5. Although the supporting structures of both embodimentshave been described with reference to the figures,

it may be emphasized that C-shaped cantilever beams are provided whichsurround the upper and lower header pipes, as shown in FIGS. 1 and 2,and are secured to the transformer tank wall so as to transmit thevertical load to the wall. The weight of the radiator block actuallyrests on the plates interposed between the lower C- shaped beam 12 andthe tank wall 8.

In FIGS. 4 and 5, there are no cantilever beams (that is, beams clampedon one end only) but girders with a C-shaped cross-section. The upperones preferably serve for transporting one or more radiator blocks bymeans of a crane (e.g., during installation or repair), while the lowerones are adapted to mount the radiator installation onto a separatefoundation or base (as shown in FIG. 4 in broken lines). The attachmentof the individual radiator batteries to the girders can be provided innumerous conventional ways, and this is a structural expedient wellknown to those skilled in this art.

In order to feed a maximum number of radiator blocks (as shown in FIGS.1 and 2) at a given length of the header members 21, 22, as it is shownin FIG. 6, pipe connections 24 to flanges 25, for joining the U-shapedheader members 1, 5 to the headers 21, 22, are made slanting to theright and to the left, respectively, from the main headers 21, 22, andare symmetrically staggered with regard to the central plane of theradiator block (FIG. 5). Owing to the symmetrical arrangement of thepipe connections 24, equal flow resistances result for each of tworadiator blocks lying in parallel (top and bottom in FIG. 5) for the oilstream from the upper headers 1 to the lower headers 5. Finally, at 23expansion pipes are indicated between the main headers 21, 22 and theouter wall of the transformer tank 8, by means of which unavoidableinaccuracies of assembly or thermal expansions may be compensated for.

FIG. 7 shows the first two radiator elements connected to the respectivedistributing and collecting headers 21 and 22, with the pipe elbows 9protruding from the re spective top and bottom header pipes 1 and 5.

It will be understood that features described and illustrated for thefirst embodiment (FIGS. 1 to 3) are also 1. applicable to the secondembodiment (FIGS. 4 to 7). Thus, the riser sections 2, 3 and 4 may besupplemented by innermost riser sections 10 and pertaining short pipesections 11, connected to the header members 1, 5 as shown in FIG. 3.Elbows 9 are shown in FIGS. 5 and 7 for riser sections 4, as in FIG. 2.

Also, flanges 6 and shut-off devices 7 are employed between the mainheaders 21, 22, on the one hand, and the transformer tank 8, on theother, in addition to, or instead of the illustrated expansion pipes 23(as shown for the header members 1, 5 of FIGS. 1 to 3).

FIGS. 4, 5 and 7 also show the forced-cooling fans 17 and their mountingflanges 16; the pertaining terminal boxes 18 and their attachments 19are exemplified in FIG. 2 only but are of course applicable to thesecond embodiment as well.

It may be summarized that the embodiment of FIGS. 4 to 7 ischaracterized by the distributing and collecting main headers 21, 22before and after the U-shaped header members 1, 5, when considering thedirection of the oil flow. The arrows in the drawings clearly show thedirection of the natural or thermosiphon oil circulation. This actuallyconstitutes a combined series-parallel connection for the various oilpaths. The series connection relates to the oil flow in axial directionof the main headers, in combination with the flow in the direction ofeach leg of the U-shaped header member (both at the distributing and atthe collecting side). Each parallel connection or path actually bisectsthe flow resistance in a known manner (analogous to the parallelconnection of electrical resistors). The principle of parallelconnections starts with the pipe connections and flanges 24, 25 wherethe first bifurcation of the oil flow takes place, and then it continuesin the U-shaped header members 1 where the oil stream branches off tothe two limbs of the U.

It will be understood that the individual header members 1 and 5 ofFIGS. 4 to 7 may also have flanges connected to the straight portions,between the two limbs or legs, and these flanges may be similar to thoseshown in FIG. 2 with numeral 6. When considering the top elevationalview of FIG. 5, it will be seen that the branching off of the oil flowfrom the top or distributing header 21 alternates between the twoopposite rows of radiator blocks (upper and lower rows, as shown in thedrawing). This makes for optimally uniform distribution of the warm orheaded-up oil among the individual radiator units. The bottom orcollecting header 22 has a similar arrangement with respect to theheader members 5 connected thereto (see also FIG. 4);

Compared with known radiator structures, the cooler arrangement inaccordance with this invention makes it possible to provide a greaternumber of cooling elements with a given required space, or to accomplishthe oil circulation with less resistance to the oil flow with a givennumber of cooling elements. In doing so it becomes possible to eliminatethe heat due to transformer losses, even with large transformercapacities, only by air-cooled radiators, possibly even without forcedcooling by fans.

Moreover, compared with similar known radiator arrangements, the numberof shut-off devices and packings is essentially reduced, maintaininggood interchangeability and accessibility of the cooling elements whichform an assembly unit. This is an advantage in regard to maintenance,repair and supervision, and also reduces the material and labor costs.

A substantial number of transformer-cooling radiator units can besupplied with oil, even at low flow velocities, particularly when usingthe second embodiment of the invention, as described hereinabove. Thenumber of such units is considerably higher than could be attained withhitherto known devices. The inventive arrangement allows to dissipatethe heat of very large transformers by the natural circulation of thecooling oil, as described earlier, entirely without, or only withintermittent, forcedair cooling.

It is important in the inventive cooling arrangement to keep the surfaceat a maximum which is available for the heat exchange between thewarmed-up transformer oil flowing from the upper transformer tankportion toward the radiator elements. This is of course enhanced by theabove-described series-parallel connection of the oil flow paths, whilethe cooling air sweeps along the individual riser sections in an upwarddirection (that is, countercurrent to the downwardly oil flow), eitheras a result of natural draft (actually a chimney effect) or on accountof the forced-cooling fans. Oil and air-fiow arrows are shown in FIG. 1.

While keeping the heat-exchange surface at a maximum, care has to betaken not to allow the flow resistance of the oil stream to reachexcessively high values on account of the repeated ramification orbranching effect, which could eventually render ineffective theincreased cooling surface. In other words, it is important to achieve acompromise between the size of the cooling surface and the flowresistance by which maximum heat dissipation can be achieved. It is notenough to provide a series connection of any desired number of coolingelements if this should re salt in an increase of the oil flowresistance to a value which would then tend to decrease the coolingcapacity as an end result.

The double-sided oil supply provided by the U-shaped header members,forming the important feature of both described embodiments, isconsidered to be an essential factor in achieving the optimum compromisepossible in such cooling arangements. The multiple set-up of the secondembodiment provides even better results than the first one as a resultof the described combined and multiple oil paths. There is of course theadded advantage of accommodating a large number of radiator units in arelatively limited space, which has serious economic benefits in suchinstallations.

The foregoing disclosure relates only to preferred, exemplaryembodiments of the invention, and to applications thereof, which isintended to include all changes and modifications of the examplesdescribed within the scope of the invention as set forth in the appendedclaims.

What we claim is:

1. A cooling arrangement for dissipating the heat produced by losses inan oil-filled electric transformer or reactor, the latter including anoil tank, the arrangement comprising at least two groups of a pluralityof substantially vertical riser sections to and from which the oil to becooled is supplied from said tank in parallel connection, by way of atleast two pairs of substantially horizontal, U-shaped upper distributingand lower collecting header members having each a base of the U and twoflanking legs between which said riser sections are connected, upperdistributing and lower collecting main header pipes in seriescommunication between said tank and said header members, the latterbeing connected on opposite sides of said main header pipes,substantially at the middle of their bases, and facing in oppositedirections, alternately laterally slanting pipe connections between saidheader members and at least one of said main header pipes, and means forsupporting said header members from the wall of said tank.

2. The cooling arrangement as defined in claim 1, further comprisingshort pipes welded to said base of the U- shaped header members forproviding connection to at least one of said riser sections.

3. The cooling arrangement as defined in claim 1, further comprising aflange and a shut-off device attached to said base of the -U-shapedheader members for providing selectively operable communication to saidmain header plpes.

4. The cooling arrangement as defined in claim 1, further comprising apipe elbow attached to one of said riser sections for connection to theouter ends of said header members.

5. The cooling arrangement as defined in claim 1, wherein said mainheader pipes have a cross-section tapering off from the side of saidtank toward the outermost one of said header members.

6. The cooling arrangement as defined in claim 1, further comprising anexpansion pipe between said tank and at least one of said main headerpipes.

7. The cooling arrangement as defined in claim 1, further comprisingmeans for forced air cooling of at least some of said riser sections ina substantially vertical, upward direction, countercurrent to thedownward flow of the oil to be cooled within said riser sections.

References Cited UNITED STATES PATENTS 2,024,716 12/ 1935 Brown -473,016,230 -1/1962 Cedarstrom et al. 165-175 X 3,235,823 2/ 1966 Renberg336-58 X FOREIGN PATENTS 687,592 4/ 1930 France.

1,267,122 6/ 1961 France.

7,695 1914 Great Britain.

679,241 9/1952 Great Britain.

886,489 1/ 1962 Great Britain.

209,015 3/ 1940 Switzerland.

ROBERT A. OLEARY, Primary Examiner. A.W. DAVIS, Assistant Examiner.

1. A COOLING ARRANGEMENT FOR DISSIPATING THE HEAT PRODUCED BY LOSSES INAN OIL-FILLED ELECTRIC TRANSFORMER OR REACTOR, THE LATTER INCLUDING ANOIL TANK, THE ARRANGEMENT COMPRISING AT LEAST TWO GROUPS OF A PLURALITYOF SUBSTANTIALLY VERTICAL RISER SECTIONS TO AND FROM WHICH THE OIL TO BECOOLED IS SUPPLIED FROM SAID TANK IN PARALLEL CONNECTION, BY WAY OF ATLEAST TWO PAIRS OF SUBSTANTIALLY HORIZONTAL, U-SHAPED UPPER DISTRIBUTINGAND LOWER COLLECTING HEADER MEMBERS HAVING EACH A BASE OF THE U AND TWOFLANKING LEGS BETWEEN WHICH SAID RISER SECTIONS ARE CONNECTED, UPPERDISTRIBUTING AND LOWER COLLECTING MAIN HEADER PIPES IN SERIESCOMMUNICATION BETWEEN SAID TANK AND SAID HEADER MEMBERS, THE LATTERBEING CONNECTED ON OPPOSITE SIDES OF SAID MAIN HEADER PIPES,SUBSTANTIALLY AT THE MIDDLE OF THEIR BASES, AND FACING IN OPPOSITEDIRECTIONS, ALTERNATELY LATERALLY SLANTING PIPE CONNECTIONS BETWEEN SAIDHEADER MEMBERS AND AT LEAST ONE OF SAID MAIN HEADER PIPES, AND MEANS FORSUPPORTING SAID HEADER MEMBERS FROM THE WALL OF SAID TANK.